The efficiency of an optical device (e.g., the aspects of the drive voltage or power requirement of the device) is fundamentally determined by the electro-optic materials used to construct the device. Silicon materials are more easily processed and more readily available, but are not as efficient at light emission or absorption as non-silicon materials (such as III-V materials), nor do they possess other desirable optical properties present in materials such as, magneto-optic materials, and other crystal substrate materials. Attempts have been made to create photonic devices utilizing these materials in addition to silicon, wherein the device's optical waveguide is formed and included silicon semiconductor material and non-silicon material (and, in some cases, the bonding layer combining both materials). These devices are referred to herein as heterogeneous photonic integrated circuits (PICs).
Heterogeneous PICs on silicon-on-insulator (SOI) substrates require a method of controlling the confinement factor of the optical mode in the heterogeneously integrated material. It is desirable to be able to achieve a wide range of optical confinement factors in the heterogeneous material, nearly spanning 0 to 100%, in order to efficiently transfer light between Si-only modes and heterogeneous modes, to avoid interaction of light with absorbing or scattering materials and structures, and to optimize optical and optoelectronic devices for characteristics dependent upon confinement factor of the mode in the heterogeneous material such as gain, saturation, absorption coefficient, nonlinear coefficients, and modulation efficiency per unit distance.
Current solutions rely on controlling the optical confinement in the heterogeneous material by laterally varying the dimension of either the silicon waveguide, the heterogeneous material, or both. The drawback of these approaches is that the flexibility to change confinement in the heterogeneous integrated material is dependent on the range of widths for which one can define the structures. The range of widths is restricted by lithography for both silicon waveguides and the heterogeneous integrated materials. In the case of active devices, the range of widths is additionally restricted by device design considerations such as the maximum width permissible to obtain the desired capacitance and current density, and the minimum width permitted to create electrical contacts and current channels.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the invention is provided below, followed by a more detailed description with reference to the drawings.